Field of the Invention
The present invention relates to a dynamic damper provided in a drive shaft of a vehicle to reduce booming noise occurring when a bending mode of the drive shaft coincides with an excitation frequency of an engine, and, more particularly, to a dynamic damper assembly capable of reducing noise in a multi-frequency band even though only one dynamic damper is mounted to a drive shaft.
Description of Related Art
In general, vibrations occur in a structure or a device when an external force is applied thereto, regardless of whether the structure or the device has or does not have its own power.
For example, when an external force is applied to a device for generating power by transferring explosive power from a four-stroke engine of a vehicle to drive wheels through drive shafts via a transmission, or a structure which does not have its own power, vibrations occur in the device or the structure. These vibrations deteriorate the mounting safety of the engine or structure, and cause interference when the components or related parts thereof are operated, which may lead to the deterioration of accuracy or the risk of malfunction.
The drive shafts for transferring such a driving force are installed between the transmission fixed to a frame and the drive wheels fixed to chassis springs. For this reason, the drive shafts cause bending vibrations such as torsion and whirling, and the explosive vibration of the engine is applied to the drive shafts.
Particularly, a differential is one-sided in a Front-engine Front-drive (FF) vehicle, with the consequence that a Left Hand (LH) drive shaft has a short length and a Right Hand (RH) drive shaft has a long length, as illustrated in FIG. 1. Accordingly, the RH shaft has a low bending natural frequency due to the long length thereof, and booming noise thus occurs when the RH shaft resonates in the excitation range of an engine.
In order to attenuate a resonant frequency and improve Noise, Vibration and Harshness (NVH), a dynamic damper is mounted to the drive shaft. However, since a typical dynamic damper is set to attenuate a single frequency, a secondary anti-resonant phenomenon may occur before and after the frequency attenuated by the dynamic damper.
In order to reduce such secondary anti-resonance, vehicles use dampers made of a material having a relative large loss factor. However, there is a limit to the attenuation of anti-resonance using such materials, and a desired frequency may be offset in a low-temperature region (at a temperature equal to or less than 0° C., or in a cold region) since the rate of change in natural frequency is increased according to a change in temperature. In addition, two dynamic dampers may be mounted to a vehicle in which a considerable degree of secondary anti-resonance occurs, but this is disadvantageous in terms of increases in weight and cost.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.